A187680 - OEIS

A187680

a(n) = (product of divisors of n) mod (sum of divisors of n).

0, 2, 3, 1, 5, 0, 7, 4, 1, 10, 11, 20, 13, 4, 9, 1, 17, 21, 19, 20, 25, 16, 23, 36, 1, 4, 9, 0, 29, 0, 31, 8, 33, 22, 25, 83, 37, 4, 9, 40, 41, 48, 43, 8, 21, 28, 47, 88, 1, 8, 9, 76, 53, 96, 1, 16, 49, 34, 59, 120, 61, 4, 31, 1

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OFFSET

1,2

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

FORMULA

a(n) = A007955(n) mod A000203(n).

a(n) = 0 iff n is in A145551 and a(n) = 1 iff n is in A188061. - Amiram Eldar, Jun 18 2022

MAPLE

A187680 := proc(n) A007955(n) mod numtheory[sigma](n) ; end proc:

seq(A187680(n), n=1..120) ; # R. J. Mathar, Mar 17 2011

MATHEMATICA

Table[Mod[Times@@Divisors[n], DivisorSigma[1, n]], {n, 70}] (* Harvey P. Dale, May 23 2021 *)

a[n_] := Mod[n^(DivisorSigma[0, n]/2), DivisorSigma[1, n]]; Array[a, 60] (* Amiram Eldar, Jun 18 2022 *)

PROG

(PARI) a(n) = my(d=divisors(n)); vecprod(d) % vecsum(d); \\ Michel Marcus, Jan 29 2019

CROSSREFS

Cf. A000203, A007955, A145551, A188061.

Sequence in context: A264638 A201737 A080063 * A328731 A140706 A200068

Adjacent sequences: A187677 A187678 A187679 * A187681 A187682 A187683

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Mar 17 2011

STATUS

approved